Inhalers provide an alternative drug-delivery method that permits patients to aspirate medication rather than swallow a pill, or drink or inject medication. In some cases, such as with medications that directly target the patient's lungs, aspiration enables the medicine to reach the target area more quickly. In addition, aspiration is typically considered to be less painful than other drug-delivery methods.
Many inhalers rely upon mechanical atomizers or a pressurized cartridge to dispense medication. The dose delivery of such mechanisms can be dependent upon the force exerted on the activation mechanism, the pressure of carrier gas, and the inhalation force exerted by the user. As such, the dose delivery is generally imprecise, and such inhalers are typically only useful with medications having a broad dosage tolerance.
As an alternative, electronic inhalers, such as those that utilize bubble jet or piezoelectric ejectors to dispense medication, may offer a more advantageous method of dose delivery. However, a positive medication pressure may result in medication leaking from the ejector orifices of the inhaler. The inhaler may therefore keep the medication at a slight back or negative gauge pressure. However, too much back pressure may result in the ejectors of the inhaler being starved of medicament, and “deprimed”. If the ejectors are deprimed in this way, the inhaler may subsequently misfire, resulting in inaccuracy in the ejected dose. Excessive back pressure may also cause air to be sucked into the inhaler when not in operation, causing air bubble entrapment that can lead to ejection problems and/or errors in dosage.
In addition, variations in the pressure of the medication supply used by the inhaler may still alter the dosage delivered over the lifetime of the supply. Variations in medication pressure may also effect the size of the individual droplets generated by the inhaler. Droplets that are too small may not be retained by the lungs, and may be exhaled out of the body instead. Similarly, droplets that are too large may not be absorbed by the lungs, and may also be exhaled out of the body.